U.S. Pat. No. 6,661,509 describes exemplary devices and methods for attaining alignment of optical beams in spectroscopic microscopes, and these devices and methods will now be summarized with reference to the accompanying FIG. 1. It should be understood that this is only a brief summary, and more details can be found in U.S. Pat. No. 6,661,509, which is incorporated by reference herein such that its contents should be regarded as a part of this document.
A spectroscopic microscope system, designated generally by the reference numeral 10, includes an optical microscope depicted within the phantom/dashed lines 11. The microscope 11 includes an objective optical element 12 and an ocular optical element 14 (here depicted as lenses, though reflective elements, e.g., mirrors, could be used instead of refractive elements such as lenses). Light from a sample located at a sample position 16 is transmitted through the objective optical element 12 to the ocular optical element 14 on a microscope beam path 17 to form an image that can be viewed by a viewer either directly through the ocular optical element 14, or with the use of video camera 15 and a video display terminal (not shown).
Molecular spectrometry may also be performed on the sample. An illuminating light beam 21 is provided from a light source 20 (depicted here as a laser, though other light sources may be used) through a beam path adjuster 22 to a mirror 24 which redirects the illuminating beam 21 on a path toward the mirror 26. The mirror 26 deflects the illuminating beam 21 onto a path coincident with the microscope beam path 17. The objective lens 12 focuses the illuminating beam 21 onto a focal point 28, thereby causing any sample at this point to interact with the illuminating beam 21 and scatter, emit, or otherwise deliver light having different wavelength content along return beam path 30 after being collected by the objective optical element 12. The return beam 30 is deflected by the mirror 26 onto a path coincident with the illuminating beam path 21, and is allowed to pass through mirror 24 (which is a dichroic mirror chosen to pass wavelengths along one or more ranges other than those of the illuminating beam 21). The return beam 30 passes through a beam path adjuster 34 (i.e., a set of optical elements capable of shifting the axis of the return beam 30), and through an input lens 35 which focuses the beam 30 onto the spectrograph input aperture 36 of spectrograph 37. The spectrograph 37 may be formed to spatially distribute the wavelengths of light in the return beam 30 (e.g., by a Czerny-Turner monochromator or other arrangement, not shown), with the wavelengths then being incident upon a detector 38 which detects the intensity of the light at the various wavelengths to provide an output signal which characterizes properties of the sample.
The beam path adjusters 22 and 34 are provided in order to precisely align the illuminating beam 21 and return beam 30 with the focal point 28 and spectrograph input aperture 36. These are fed adjustment signals by a control system 44, which relies on input from detector 38 (as discussed below) and from an alignment unit 39 situated on or within the sample stage 40 of the microscope 11. The alignment unit 39 includes a stage entrance aperture 41 which is positioned by the operator, by viewing the alignment unit 39 with the ocular optical element 14 and/or video camera 15, to coincide with the central axis of the microscope optical beam 17. The alignment unit 39 includes with its interior a stage light source 60, e.g., a high intensity light emitting diode (LED), actuated by line 62 communicating with control system 44, and a stage light sensor 65, e.g., a silicon photodiode situated to receive light transmitted through the LED/stage light source 60, with the stage light sensor 65 emitting a stage light sensor output signal to control system 44 along line 68 in response to receipt of light. The control system 44 performs alignment by turning on the stage light source 60 and then adapting the beam path adjuster 34 until the return beam 30 from the stage light source 60 registers with maximum intensity on the detector 38, thereby indicating that such a return beam 30 would also be well-aligned with the spectrograph input aperture 36 and detector 38 if the return beam 30 was generated via the illuminating light beam 21 from the light source 20. Similarly, the beam path adjuster 22 can be adapted by the control system 44 until the stage light sensor 65 measures maximum output from the light source 20, indicating that the illuminating light beam 21 is properly aligned. In other words, the input or datum beam 21 for spectrometry is optimized via beam path adjuster 22 by signals from the stage light sensor 65 in the alignment unit 39 (with the stage light sensor 65 being stimulated by the light source 20), and the return beam 30 for spectrometry is optimized via beam path adjuster 34 by signals from the detector 38 in the spectrograph 37 (with the detector 38 being stimulated by the stage light source 60). Note that the control system 44 communicates with the light source 20 by line 46, with the beam adjuster 22 by line 47, with the detector 38 by line 48, and with the beam adjuster 34 by line 49, as well as with the stage light sensor 65 via line 68 and the stage light source 60 via line 62. Once alignment is achieved, the alignment unit 39 may be removed from the sample stage 40 (if not built therein) so that the microscope system 11 may be used for analyzing samples.
The foregoing arrangement is beneficial, but it still has limitations. In particular, alignment of the alignment unit 39 (more particularly its stage entrance aperture 41) with the microscope beam path 17 is prone to error: since a user views the stage entrance aperture 41 through the eyepiece 14 (or via the video camera 15) and subjectively determines when the stage entrance aperture 41 is centered in the field of view, users can err in deciding when the alignment unit 39 seems to be properly situated. This in turn poses problems for adjustment of the spectrometry input beam 21 via the beam path adjuster 22, and of the spectrometry return beam 30 via the beam path adjuster 34. In particular, if the alignment unit 39 is significantly out of alignment—this misalignment being compounded by any misalignment in the beam path adjusters 22 and 34—the light from the light source 20 may not reach the stage light sensor 65 and generate a signal, and similarly the light from the stage light source 60 may not reach the detector 38 and generate a signal. Without such a signal, one cannot seek to optimize the spectrometry input and return beams 21 and 30 by seeking to maximize the signal at the stage light sensor 65 and/or detector 38. In this case, one must vary the positions of the beam path adjusters 22 and 34 and the alignment unit 39 and “hunt” for a signal at the detector 38, at which point the aforementioned methods become effective.